<template>
  <ul class="list">
    <li class="item" 
        v-for = "item of letters"
        :key = "item"
        :ref = "item"
        @click = "handleCitysArea"
        @touchstart.prevent = "handleTouchStart"
        @touchmove = "handleTouchMove"
        @touchend = "handleTouchEnd"
        >{{item}}</li>
  </ul>
</template>
<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities :Object
  },
  data () {
    return {
      touchStatus:false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  computed : {
     letters () {
        const letters = []
        for ( let i in this.cities){
          letters.push(i)
        }
      return letters
     }
  },
  methods : {
    handleCitysArea (e) {
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if(this.touchStatus){
      if(this.timer){
        clearTimeout(this.timer)
      }
      this.timer = setTimeout(() => {
        const currentY = e.touches[0].clientY - 79
        const index = Math.floor((currentY - this.startY)/20)
        if(index >= 0 && index < this.letters.length){
           this.$emit('change',this.letters[index])
        }
      },16) 
    }
  },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>
<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction:column
    justify-content: center
    position :absolute
    top : 1.58rem
    right : 0
    bottom : 0
    width: .4rem
    .item
       line-height: .4rem
       text-align: center
       color: $bgColor
</style>
